1. Technical Field
The present application relates to electronic circuit design and architecture and to devices that incorporate such electronic circuits for protection against electrical overvoltage events, and more particularly to systems, designs, circuits, methods, and materials for protecting components and devices from overvoltage electrical events and to devices incorporating such systems, designs, circuits, methods, and materials.
2. Description of Related Art
Electronic devices are often fabricated by assembling and connecting various components (e.g., integrated circuits, passive components, chips, and the like, hereinafter “chips”). Many components, particularly semiconductors, are sensitive to spurious electrical events that apply excessive voltage to the devices in what is termed an overvoltage condition. Examples of overvoltage condition sources include electrostatic discharge (ESD), back electromotive force (EMF), lightning, solar wind, solar flares, switched electromagnetic induction loads such as electric motors and electromagnets, switched heavy resistive loads, large current changes, electromagnetic pulses, spark gap, and the like. Overvoltage conditions may result in a high voltage at a device containing semiconductors such as an IC chip, which may cause large current flow through or within the chip. The large current flow may effectively destroy or otherwise negatively impact the functionality of the semiconductor. However, a system that blocks current associated with an overvoltage event from reaching the components may also impair the desired normal operation of the chip unless properly designed.
Some chips include “on-chip” protection against some overvoltage events (e.g., a mild ESD event) that may be expected during packaging of the chip (e.g., protection against Human Body Model events).
A chip may be packaged (e.g., attached to a substrate). A packaged chip may be connected to additional (e.g., ex-chip) overvoltage protection devices, that protect the packaged chip against more severe (e.g., higher voltage) overvoltage events. Inasmuch as the on-chip and off-chip overvoltage protection devices are in electrical communication, the off-chip overvoltage protection device may be required to “protect” the on-chip overvoltage protection device. Off-chip overvoltage protection devices using discrete components are difficult to add when the substrate is manufactured. Moreover, on-chip protection is difficult to optimize across a complete system or subsystem. Examples of specifications for ESD testing include IEC 61000-4-2 and JESD22-A114E.
A printed circuit board, printed wiring board, or similar substrate (hereinafter also referred to as PCB) may be used to assemble, support, and connect electronic components. A PCB typically includes a substrate of dielectric material and one or more conductive leads to provide electrical conductivity among various attached components, chips, and the like. Typically, a pattern of metallic leads is plated (e.g., using printing technology such as silk-screening) onto the dielectric substrate to provide electrical connectivity. Alternatively a metallic layer (e.g., a layer of Cu) is applied to the substrate and subsequently etched in the desired pattern. Multiple layers of conductive patterns and/or dielectric materials may be disposed on a PCB. The layers may be connected using vias. Printed circuit boards including 14 or more layers are not uncommon.
A PCB is typically used for supporting and connecting various integrated electronic components, such as chips, packages, and other integrated devices. The PCB may also support and connect discrete components, such as resistors, capacitors, inductors, and the like, and provide connections between integrated and discrete components. The conductive patterns and/or layers in the PCB and other components or areas within electronic devices sometimes provide paths for conducting overvoltage events that could damage or otherwise negatively impact components.